1. Field of the Invention
The invention relates to copiers, and more particularly to copiers that use disposable ribbon cartridges, such as portable copiers.
2. Description of Related Art
Portable printing devices, such as copiers, printers, typewriters and facsimile machines, frequently use replaceable components, such as ribbon cartridges and batteries. To maximize the efficiency of these printing devices, a high number of output pages per ribbon cartridge and per battery charge is desirable.
In typical plain paper facsimile machines using thermal transfer technology, a ribbon cartridge may contain enough ribbon to make 100 to 300 standard-size copy sheets before the ribbon cartridge needs to be replaced. In many such devices, which can also be used as copiers as well as fax machines, replacing the ribbon cartridge requires opening a portion of the device to access the ribbon cartridge and separating the nips holding the copy sheet, disturbing its position. If the ribbon runs out in mid-sheet, therefore, as often happens, the copy sheet being printed upon when the ribbon runs out must be discarded and the corresponding document recopied. This wastes ribbon, paper, and power. A need has arisen, therefore, for a copier capable of halting copy sheet advance and allowing ribbon cartridge replacement without disturbing the copy sheet position, or, for that matter, the position of the original document.
Previous copiers also include inefficiencies in the drive trains of their components. In U.S. Pat. No. 5,187,588 to Stemmle, for example, the disclosure of which is incorporated herein by reference, a motor drives a scan carriage along a linear reciprocating path, causing the scan carriage to engage followers, which turn two barrel cams and cause document and copy sheet index shafts to rotate so as to advance the document and copy sheet. Thus, rotary motion of a drive motor shaft is converted into linear scan carriage motion, and then the linear scan carriage motion is converted into rotary motion of document and copy sheet index shafts. Converting rotary motion to linear motion and then back to rotary motion is energy-inefficient, requiring a relatively high amount of energy, leading to rapid battery depletion.
The copier in the 588 patent also uses only a small portion of linear carriage motion to generate index shaft rotary motion (via barrel cams), contributing to system inefficiency. Additionally, carriage motion is required for every index cycle, even to advance an already-completed copy sheet from the copier. Finally, actuating both the index shafts and the scan carriage with one drive motor causes high loads on the motor, contributing to system inefficiency. There is, accordingly, a need for a more energy-efficient actuating system for portable copier document indexers, copy sheet indexers and scan carriages.
Minimizing the size of portable copiers also is desirable, preferrably to a size allowing the copier to be placed in a briefcase. Placing the copier parallel to the short edge of the briefcase allows room for other contents. Surveys of standard briefcase sizes have shown that if the length of a portable copier can be kept below 11.7 inches, it will fit into over 80% of standard briefcases, parallel to the short edge. Previous portable copiers, however, all have maximum dimensions that are far in excess of this dimension.
One architectural feature affecting overall copier length is the alignment of the document relative to the copy sheet. Offset between the document and the copy sheet increases overall copier length by the amount of the offset. A second contributor to overall copier length for copiers using thermal transfer technology is ribbon cartridge size. Space must be made available for both the take-up roll and the supply roll of ribbon. If the ribbon rolls are mounted on the scan carriage, requiring separate areas for placement of the take-up and supply rolls, each area must contain sufficient space to hold the maximum diameters of both the supply and take-up rolls. This is in spite of the fact that the supply and take-up rolls never simultaneously occupy their maximum space. Finally, while the image sensing component could be positioned directly on top of the printhead component, this would require that the take-up and supply rolls be positioned on opposite sides of these components. Thus, the width of the imaging components as well as two full diameters of the ribbon rolls increase the overall length of the product. There is, accordingly, a need for a portable copier of reduced length.
Finally, in previous designs, indexing the copy sheet out of the copier requires moving the scan carriage and thus advancing the ribbon in the ribbon cartridge. When copying short documents onto a full-sized piece of copy sheet, therefore, advancing the copy sheet wastes ribbon and battery power. There is a need, therefore, to index the copy sheet independently of carriage motion.
U.S. Pat. No. 4,476,496 to Thaler shows a linear motor facsimile machine in which a motor-driven reciprocating block supports a printhead for printing on paper.
U.S. Pat. No. 4,823,195 to Ito shows a recording apparatus in which a ribbon cassette mounted on a reciprocating carriage supplies ink to a copy sheet. The copy sheet advances along a copy sheet path adjacent the carriage.